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= = = = = = = = = = = **Chapter 2: Section 1** = ** http://sportsnation.espn.go.com/fans/SportScience_JohnBrenkus/blog#/fans/SportScience_JohnBrenkus/blog/posts/122596 ** ** - In this article on ESPN Sports Science's John Brenkus disc **usses about the force of hits in football "ruining" the sports. He tries to convince the football world that just because they discourage "big hits" in football, it will still be the same sport, only safer. In this article, Brenkus talks about the science of this situation using weight, speed and force. "For example, two 190-pound players going just 13 mph can generate over 90gs in a head to head collision. This over four times the amount of force necessary to fracture your neck." This uses math and science to show the public the severeness of the hits football players take every day.
 * November 8, 2010 Homework:**

**What Do You Think?**  November 8, 2010  - They are able to keep moving across the ice at high speeds for long periods of times because of the way their skates glide across the ice and when you have a fast start, the rest is a lot easier. Depending on the momentum behind the kick of the soccer ball, the ball constantly moves until all of the force is gone.

**Investigate**  November 8, 2010

 Hypothesis: **The vertical height would be the same on each side because the force exerted is equal**  1d: **5.33 meters**  1e: **5.31 meters**  2a: **He will reach his same position on the opposite side of his initial position. I think this because since he has more room to "skate" and his slope was not decreased enough, he will be higher on the other side.**  3a: **We were correct because we changed the track and knew the position of the track in relation to it's opposite time.**  3b: **Vertical height of ball = 5.29 meters. The ball moved down the initial slope and then went up the other side to the exact same point as to where it started except it was on the opposite time.**  4a: **Now that the slope is less steep, he will not go up as high as his initial position on the opposite side.**  4b: **We predicted wrong, he went almost a meter higher than where he originally started on the opposite side.**  5a: **No because he will never change direction.** <span style="font-family: Arial,Helvetica,sans-serif;"> 5b: **He will keep rolling until the force behind him has completely decreased.** <span style="font-family: Arial,Helvetica,sans-serif;"> 5c: **He would keep on moving** <span style="font-family: Arial,Helvetica,sans-serif;"> 5d: **Our prediction was correct. The skater eventually stops when the force behind him is gone and he is not on the track anymore.** <span style="font-family: Arial,Helvetica,sans-serif;"> 6a: **The length of the opposite track increases** <span style="font-family: Arial,Helvetica,sans-serif;"> 6b: **It increases as the slope decreases** <span style="font-family: Arial,Helvetica,sans-serif;"> 6c: **It is the same** <span style="font-family: Arial,Helvetica,sans-serif;"> 6d: **He would not stop since there was no friction.**

<span style="font-family: Arial,Helvetica,sans-serif;">**Physics Talk Summary** <span style="font-family: Arial,Helvetica,sans-serif;"> November 8, 2010 <span style="font-family: Arial,Helvetica,sans-serif;">__Galileo:__ <span style="font-family: Arial,Helvetica,sans-serif;"> - An object at rest, remains at rest, unless something causes it to move. <span style="font-family: Arial,Helvetica,sans-serif;"> - __Inertia:__ the natural tendency of an object to remain at rest or to remain moving with a constant speed in a straight line / property of matter that resists changes in motion. > <span style="font-family: Arial,Helvetica,sans-serif;">measured in mass ; units are kilograms <span style="font-family: Arial,Helvetica,sans-serif;">- __Newton's first law of motion:__ in the absence of an unbalanced force, an object at rest remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path. <span style="font-family: Arial,Helvetica,sans-serif;"> - __Frames Of Reference:__ relative to values - adding or subtracting velocities. <span style="font-family: Arial,Helvetica,sans-serif;"> - __Running Starts__: increased distance or speed to give an advantage

<span style="font-family: Arial,Helvetica,sans-serif;">**Checking Up Questions:** <span style="font-family: Arial,Helvetica,sans-serif;"> 1) The natural tendency of an object to remain at rest or to remain moving with a constant speed in a straight line. <span style="font-family: Arial,Helvetica,sans-serif;"> 2) Newton's first law of motion states that without force, an object stopped with stay stopped and an object moving will keep on moving. <span style="font-family: Arial,Helvetica,sans-serif;"> 3) Force (a push or pull ; unbalanced force) <span style="font-family: Arial,Helvetica,sans-serif;"> 4) The friction on the floor, or a different type of force, will stop the motion of the ball. <span style="font-family: Arial,Helvetica,sans-serif;"> 5) The larger mass will have the greater intertia. <span style="font-family: Arial,Helvetica,sans-serif;"> 6) Because the train is also moving, which means calculating the speed of the ball, you need to subtract the speed of the train: tells you from the perspective at which you are looking at it from.

<span style="font-family: Arial,Helvetica,sans-serif;">**Physics To Go:** <span style="font-family: Arial,Helvetica,sans-serif;"> 1) <span style="font-family: Arial,Helvetica,sans-serif;"> a: It will go on forever <span style="font-family: Arial,Helvetica,sans-serif;"> b: Because there is no force to stop the ball (such as friction), the ball has no "reason" to stop. <span style="font-family: Arial,Helvetica,sans-serif;"> 2) It will reach a vertical height of 20 cm <span style="font-family: Arial,Helvetica,sans-serif;"> 3) I don't think that is possible because we always have gravity and friction, no matter where we go. There is only less or more of the force never none. <span style="font-family: Arial,Helvetica,sans-serif;"> 4) Once hit, the hockey puke slides across the ice due to the force behind it, when it hits another player's stick it slightly bounces off but stops due to the force it just hit. <span style="font-family: Arial,Helvetica,sans-serif;"> 5) 2.5 + 4.5 = 7 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> 6) 10.3 + 4.2 = 14.5 meters per second relative to the ground <span style="font-family: Arial,Helvetica,sans-serif;"> 7) <span style="font-family: Arial,Helvetica,sans-serif;"> a: The cart's velocity relative to the ground is (5.6+2.4) 8 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> b: The cart's velocity relative to the tracks when moving towards the rear of the car is (5.6-2.4) 3.2 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> c: The car's velocity relative to the ground is (5.6^2+2.4^ = 37.1, sqrt37.1) 6.1 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> 8) 85-18 = 67 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> 9) <span style="font-family: Arial,Helvetica,sans-serif;"> a: 15/sin(45) = 21.21 cm <span style="font-family: Arial,Helvetica,sans-serif;"> b: 15/sin(20) = 43.86 cm <span style="font-family: Arial,Helvetica,sans-serif;"> c: 15/sin(15) = 57.96 cm <span style="font-family: Arial,Helvetica,sans-serif;"> d: 15/sin(5) = 172.11 cm <span style="font-family: Arial,Helvetica,sans-serif;"> 10) <span style="font-family: Arial,Helvetica,sans-serif;"> a: Football sitting on a stand - waiting for someone to kick it (saying at rest). The glove of a baseball player waiting to catch a ball. <span style="font-family: Arial,Helvetica,sans-serif;"> b: A sports caster would be more dramatic about the situation and probably would not be talking about the physics of the moment in the sport.

<span style="font-family: Arial,Helvetica,sans-serif;">**What Do You Think Now:** <span style="font-family: Arial,Helvetica,sans-serif;"> - Figure skaters keep moving across the ice at high speeds because the ice has very little friction, making it easier for them to move for longer times. A soccer ball continues to roll after being kicked until another force stops it. They horizontal speed is determined by the force behind the movement. The ice-skater keeps moving because of the very low friction on the ice and the constant moving of their feet. The soccer ball keeps moving because of the friction behind it and the fact that nobody else's force is trying to stop it.

<span style="font-family: Arial,Helvetica,sans-serif;"> - How relative motion depends on the speeds of the player and the ball and the reference frame in which it is measured.

<span style="font-family: Arial,Helvetica,sans-serif;">**Inquiring Further:** <span style="font-family: Arial,Helvetica,sans-serif;">__Sliding into Base:__ Baseball players do not slide into first base because they do not have as great as a running start. They have less force behind their run because they just exerted so much energy into hitting the ball. Also because players can run past first place without getting out. Your momentum is decreased when you slide into a base, but at first place it is okay to increase your momentum and run past the base. <span style="font-family: Arial,Helvetica,sans-serif;"> (http://answers.yahoo.com/question/index?qid=20090823160105AA4GAAd)

=<span style="font-family: Arial,Helvetica,sans-serif;">Chapter 2: Section 2 =

<span style="font-family: Arial,Helvetica,sans-serif;">**What Do You Think:** <span style="font-family: Arial,Helvetica,sans-serif;"> 100 miles per hour is a very fast time, along with 45 meters per second. It is very stressful for a baseball player, or any person, to have their mind think as fast as the ball (or any object) is moving.

<span style="font-family: Arial,Helvetica,sans-serif;">**Physics Talk Summary:** <span style="font-family: Arial,Helvetica,sans-serif;"> -Average speed is the distance traveled divided by the time taken to travel that distance - long distances or times over which there may be variations (Vav = Vi + Vf / 2) <span style="font-family: Arial,Helvetica,sans-serif;"> -Acceleration is a change in the direction of motion - how fast speed changes <span style="font-family: Arial,Helvetica,sans-serif;"> >Calculate: divide the change in speed by the time interval during which the change took place. <span style="font-family: Arial,Helvetica,sans-serif;"> - Instantaneous speed is the speed at that moment <span style="font-family: Arial,Helvetica,sans-serif;"> -Positive Acceleration - increasing speed <span style="font-family: Arial,Helvetica,sans-serif;"> - Negative Acceleration - decreasing speed

<span style="font-family: Arial,Helvetica,sans-serif;">**Checking Up Questions:** <span style="font-family: Arial,Helvetica,sans-serif;"> 1) <span style="font-family: Arial,Helvetica,sans-serif;"> a: __constant speed:__ the whole graph is evenly spaced <span style="font-family: Arial,Helvetica,sans-serif;"> b: __positive acceleration:__ slowly get higher (dots get farther apart) <span style="font-family: Arial,Helvetica,sans-serif;"> c: __negative acceleration:__ the graph slowly gets lower (dots get closer together) <span style="font-family: Arial,Helvetica,sans-serif;"> 2) 400/50 = 8 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> 3) Instantaneous speed is the speed at an exact moment but average speed is the average of instantaneous speeds through out a whole trip. <span style="font-family: Arial,Helvetica,sans-serif;"> 4) 10/3600 = .0028 <span style="font-family: Arial,Helvetica,sans-serif;"> 100/.0028 = 3600 km/h^2

<span style="font-family: Arial,Helvetica,sans-serif;">**Physics To Go:** <span style="font-family: Arial,Helvetica,sans-serif;"> 1. Instantaneous speed is the speed at a given moment, where average speed is the total distance traveled divided by the time it took to travel that distance <span style="font-family: Arial,Helvetica,sans-serif;"> 2) <span style="font-family: Arial,Helvetica,sans-serif;">a:1000 m / 15 s = 99.7 m/s <span style="font-family: Arial,Helvetica,sans-serif;"> b: 84 m / 6 s = 14 m/s <span style="font-family: Arial,Helvetica,sans-serif;"> c: 9.6 km / 2 h = 4.8 km/h <span style="font-family: Arial,Helvetica,sans-serif;"> d: 400 km / 4.5 h = 88.9 km/h <span style="font-family: Arial,Helvetica,sans-serif;"> 3) <span style="font-family: Arial,Helvetica,sans-serif;">a: Negative <span style="font-family: Arial,Helvetica,sans-serif;"> b: Positive <span style="font-family: Arial,Helvetica,sans-serif;"> c: None <span style="font-family: Arial,Helvetica,sans-serif;"> d: Negative <span style="font-family: Arial,Helvetica,sans-serif;"> e: None <span style="font-family: Arial,Helvetica,sans-serif;"> f: None <span style="font-family: Arial,Helvetica,sans-serif;"> 4) <span style="font-family: Arial,Helvetica,sans-serif;">a:A, D <span style="font-family: Arial,Helvetica,sans-serif;"> b: B <span style="font-family: Arial,Helvetica,sans-serif;"> c: A <span style="font-family: Arial,Helvetica,sans-serif;"> d: C <span style="font-family: Arial,Helvetica,sans-serif;">e: A +, B 0, C +/-, D + <span style="font-family: Arial,Helvetica,sans-serif;"> 6) <span style="font-family: Arial,Helvetica,sans-serif;">a: 0-45(km/h)/ = 0-12.5(m/s)/9 = -1.4 meters per second ^2 <span style="font-family: Arial,Helvetica,sans-serif;"> b: Negative <span style="font-family: Arial,Helvetica,sans-serif;"> 7) <span style="font-family: Arial,Helvetica,sans-serif;">a:Constant <span style="font-family: Arial,Helvetica,sans-serif;"> b: Speeding up <span style="font-family: Arial,Helvetica,sans-serif;"> c: Constant, Speeding up, Faster <span style="font-family: Arial,Helvetica,sans-serif;"> d: Constant, Slowing down, Speeding up <span style="font-family: Arial,Helvetica,sans-serif;"> 8. 100 mi / 2 h = 50 mi/h <span style="font-family: Arial,Helvetica,sans-serif;"> 9. No they could have had multiple speeds, but overall the average speed was 15 m/s <span style="font-family: Arial,Helvetica,sans-serif;"> 10 x-x--x---x---x---x---x <span style="font-family: Arial,Helvetica,sans-serif;"> 11. 4,8,12,16, 20 meters per second <span style="font-family: Arial,Helvetica,sans-serif;"> 14) <span style="font-family: Arial,Helvetica,sans-serif;">a: Marathon Runner <span style="font-family: Arial,Helvetica,sans-serif;"> b: Car Racing <span style="font-family: Arial,Helvetica,sans-serif;">c: Walking <span style="font-family: Arial,Helvetica,sans-serif;">d: Sprinter <span style="font-family: Arial,Helvetica,sans-serif;"> e: Jumping on a trampoline

- 100 mi/h = you travel 100 miles every hour and with 45 m/s you are moving 45 meters every second.
 * What Do You Think Now?**

-Rebounding: bouncing off of a surface and changing direction
 * Physics Plus:**

= = = = =**Chapter 2: Section 3**=

- A force is the push or pull on an object. The force behind the serve is the tennis player throwing the ball up and the force behind the racket hitting the ball. A bowling ball is much heavier than a tennis ball, so the force behind the tennis ball might hit it very far but that same force behind the bowling ball would barely move it.
 * What Do You Think:**

- __Newton's Second Law of Motion:__ Acceleration = force/mass (a=f/m) > Accelerations are caused by unbalanced forces - When two forces act at the same time the direction and the magnitude of the forces determine the motion of the object. - __Free Body Diagram:__ used to show the relative size and direction of all forces acting on an object.
 * Physics Talk Summary:**

1) Newton's Second Law of Motion states that no matter what is happening to an object, or how fast that object is going, if there is an acceleration it is completely caused by an unbalanced force. 2) When increasing an objects mass for a constant force, the acceleration will get smaller. 3) When an object weights 30 N it is exerting 30 N of force onto whatever surface it is lying upon. 4) Your weight&mass would rise just like the gravity and the acceleration
 * Checking Up:**

1) - F = 350 N - M = 80 kg - A = 10 m/s^2 - M = 80 kg - A = -15 m/s^2 - F = -3000 N 3) 42 = .30 x a 140 m/s^2 = a 4) F = .040 x 20.0 F = .8 N 5) a: The bowling ball has more inertia which means it's harder to get it to start moving and stop moving (any change in motion). b: If you want the same acceleration for the two objects, the bowling ball needs a larger force than the tennis ball to stop and start it. 9) The answer to this question depends on the force that you had behind the ball and exactly how far the ball is at at the exact time the question is talking about. 10) 40 + 50 = 90 N 11) 200 x 4 = 800 N 12) 125 = .700 x a 179 m/s^2 = a 13) sqrt(120^2 + 50^) = 130 N, 67 degrees north east 14) sqrt(5000^2 + 4000^2) = 6403 N, 39 degrees 15) F = 12.8 x 9.8 F = 125.44 N 16) a: sqrt(30^2+40^2) pheta = tan^-1 (40/3) pheta = 50 N, 53 degrees b: 50 = (5.6)a 8.9 m/s^2 = a
 * Physics To Go:**

17) a: sqrt(30^2 + 30^2) = 36 N, 34 degrees  b: 36 = 100 x a  a = .36 m/s^2  c: 50 = 100 x a  .5 m/s^2 =a

18) Volleyball: When #4 hits the volleyball with 100 N of force behind it, the other team has no chance on getting that .226 kg volleyball back to other side, so team #1 gets a point! That ball accelerated by 442.47 m/s^2, WOW!


 * Physics Plus:**

**What Do You Think Now:** - Force, unbalanced force, distance and the direction of the object affect how far an object is shown.

=Chapter 2: Section 4=

**What Do You Think:** - The force the object is thrown at and the force it might encounter during its travels it both determine how far an object thrown in to the air travels. Also gravity and the angle that is thrown at.

1) a: Yes the coins hit the floor at the same time 2) a: The coins hit the floor at the same time 3) a: No b: Yes (faster = farther) c: 4) a: The coins hit the floor at the same time, it just takes less time for the coins to get there. 5) a: I predict that the ball will fall behind of the person throwing the ball up into the air 6) a: The ball's path follows the thrower as he/she moves. The vertical component decreases of velocity on the way up and they increase on the way down. The horizontal components are unchanging. b: The factors that affect the range of the ball are speed, air-resistance and force. 7-8) __Discussion Questions:__ 1) The time increased 2) The range increased 3) The time increased 4) The range increased 5) The angle and initial speed 6) The initial height and time.
 * Investigate:**

- Projectile: the only force is the force of gravity (weight) - launched through the air. - Trajectory: path of projectional - parabolic (ground-to-ground are symmetrical around the highest point) (x and y information are independent from each other) - Free-fall: the only force is weight but its a one dimensional motion (only vertical), the vertical positions of a free-fall and a projectile are the same.
 * Physics Talk Summary:**

1) If the pen and the ruler weigh the same amount they will hit the ground at the same time. 2) No, it speeds up by 10 m/s every second. 3) The velocity when the ball is at it's highest point is 0 and it's acceleration is -9.8.
 * Checking Up:**

7) Both of arrows A and B will land on the ground at the same time. 11) The pitcher winds up, and releases the ball at breath taking speed! It travels to the player at bat who wacks it into the outfield at an outstanding distance and a great horizontal speed.
 * Physics To Go:**


 * Physics Plus:**

=Chapter 2: Section 5=

- Trajectories of projectiles vary depending on the angle that they are launched at. The higher the angle, the longer the time. The higher the speed, the less time an item takes to touch the ground.
 * What Do You Think**

- Projectiles have two motions that act at the same time yet don't effect each other. - Mathematical Model: table of times, speeds, and distances during falling - Physical Model: evenly spaced strings of calculated lengths
 * Physics Talk Summary:**

1) Constant speed across a straight line and the downwards fall of gravity at 9.8 m/s^2 2) The model must match reality in nature 3) The height increases as the range decreases.
 * Checking Up Questions:**


 * Physics Plus:**

1) 45 degree angle produces the greatest range. 2) Greater than 45 degrees = more time, less than 45 degrees = less time 3) 30 degrees = 60 degrees, 15 degrees = 75 degrees 4) This occurs because the x component is greater than the y component, the angle always has to be less than 45 degrees. Also because one is jumping, rather than running. 5) He is very good at running horizontally ( x-component) which is also involved in the long jump because you run into it and are traveling more forward rather than up. 6) a: The acceleration direction of the ball is neither up nor down, it is both of the directions working against each other at acceleration of zero. b: The velocity is zero.
 * Physics To Go:**

- A greater speed of a projectile might change the range when the launch angle is the same because the greater the speed the farther an object moving will go, and vise versa. The greater the angle, the smaller the range of the projectile, and vise versa with that as well.
 * What Do You Think Now:**

=Chapter 2: Section 6=

- When jumping, you ned to bend your knees to put all your force down through your feet to the ground. Then from there you release the force you put towards the ground, through your body, and then bounce up in the air.
 * What Do You Think:**

- __Newtons Third Law:__ for every applied force, there is an equal and opposite force. The two forces always act on different objects. >For every force applied to object A by another object B, there is an equal and opposite force applied to object B by object A >If you push or pull on something, that something pushes or bulls back on you with an equal amount of force in the opposite direction >Forces always come in pairs. - __Free Body Diagram:__ a diagram that shows the forces acting on an object and relative strength
 * Physics Talk Summary:**

1) Newtons third law of motion states that for each applied force, there will be an equal and opposite force that each act on different objects. 2) The equal force acting on earth is the gravity holding one to the ground, the opposite force on the earth is the gravity acting against the equal force, pushing you "up" 3) A free body diagram illustrates the forces that act on an object.
 * Checking Up Questions:**

1) Yes the ball does exert a force of equal and opposite force because your putting force towards the ball by holding it up, and the ball is going against that force at an equal force (and opposite) resulting in the ball staying in your hand. 2) The chair doesn't actually put a force on you, rather than it holds up your wait. Depending on the persons wait, varies how deeply the deflection that takes place. 3) The scale measures the pressure that you put on the scale and converts that, along with your acceleration, to your force (or weight). 4) The bats sometimes break because the force exerted by the ball is too great for the bat to handle, along with the balls acceleration. Another reason is that the force exerted for the bat could be too great for the ball. 5) The force exerted by the "big linebacker" impacts a "small running-back" much worse than someone of it's own size because they cannot exert an opposite and equal force. 6) The boards experience deflection when a large force hits them, and then because the player is heavier (due to it's high speed approaching the boards) the player is pushed back at a great acceleration. 7) When the baseball player wears a glove, it gives them a better chance of achieving an equal and opposite force against the ball because the glove is bigger and stronger than a naked human hand. 8) a: The bat weighs 2 pounds, traveling at 80 miles per hour. He put a total of 1,110 newtons of force into the swing, between the movement of the hips to the movement of the hands and wrists. The ball weights 145 grams. He drove that ball out of the park! The acceleration of the ball was 7.65 m/s^2. b: When a heavy ball hits a soft ground, the ground can take an impact (deflection) of the ball and bound the ball back up off the ground.
 * Physics To Go:**

- When you jump, you push down on the floor and the floor pushes up on you. The floor puts an equal and opposite force on your body which results in the upward force and then you jump into the air.
 * What Do You Think Now?**

=Chapter 2: Section 7=

- Sports such as baseball, football, track, ice-skating, dancing all require different shoes. This is because each sport has a different task one needs to complete. You need shoes better for running, or slippers for dancing.
 * What Do You Think?**

- Coefficient of Sliding Friction (µ): µ= force of friction / perpendicular force exerted by the surface on the object (normal force) > No unit of measurement > Expressed in decimal form > 0 < µ < 1 > Independent of weight > Bigger when surface is rough > Only valid for a particular pair of surfaces
 * Physics Talk Summary:**

1) You can say they are equal to each other because the force reading on the spring-scale is coming from the shoe sliding across a friction-filled surface. 2) It has no units because it is dividing Newtons by Newtons, which cancel each other out. 3) The coefficient of friction is determined by the equation mu (force of friction / normal force)
 * Checking Up Questions:**

1) During track a runner will want to increase friction between the floor and their shoes to decrease the chance of him falling during a race. During conditions such as snow or rain, the runner might need a different type of shoe to create more friction on the track. 2) Athletes desire the least amount of friction during ice skating to let them slide gracefully across the ice without friction causing them to get stuck in the ice. 3) The basketball player cannot be sure because she needs to know the type of service the other court has and the amount of friction that the surface exerts. 4) Tennis players have shoes for different surfaces to make sure that they have a good amount of friction no matter what court they are on. 5) ∑Fx = max ∑F y ma y µ f/N
 * Physics To Go:**

Np - f = ma N - w = 0 .03 = f/600 Np - 180N = 0 N = w 18 = f Np = 18 N **N = 600 N** 6) Vf = Vi + at w = mg µ = f/n ∑F y ma ∑Fx max 0 = vi + a(6) w = 1000(9.8) f = µ(n) N - w = 0 -f = ma 0 = Vi + 05.93(6) **w = 9800 N** f = (.055)(9800) N = w -5390 = 1000a 7) I think that both air resistance and water resistance change directly with the speed that you are going. 8) If there is maximum frictional force between your shoe and the track, it will effect how fast you can accelerate because the more friction there is between the two objects, the slower the track runner can accelerate. To take away this problem, the track runner needs to find shoes that exert the least amount of friction. 10) You can't walk without friction. When running you need friction between your feet and the floor so one does not slip and fall. 11) As Scott hits the baseball into the air he starts to run towards first base. The friction between his feet and the dirt help him run faster towards the base without slipping on the ground.
 * Vi = 32.34 m/s** **f = 5390 N** **N = 9800 N** **a = -5.93 m/s^2**


 * Physics Plus:**


 * Lab:**

- Some sports require different shoes because each sport needs a different type of friction between the shoe and the ground to help the athlete. Different features of a shoe would be useful for different sports because of the coefficient of friction that is found between each shoe and the type of floor/ground the shoe is rubbing against.
 * What Do You Think Now?**

=Chapter 2: Section 8=

- I believe this happens because both lengths aren't directly proportional to each other. The factors that limit the height that the pole vaulter can obtain are gravity, weight of the person, weight of the pole and wind resistance.
 * What Do You Think:**

__Pre Lab:__ a) In order to blast the penny into the air you need to place the penny at the top of the ruler and pull back the ruler (while the ruler is placed vertically or horizontally). The height of the penny depends on the bend of the ruler. You need to press down on the ruler fast and let the penny bounce into the air. b) The factors that determine the height of the penny is the speed you hit the ruler with, the force you use, the deflection of the ruler, the placement of the penny on the ruler, mass of the penny __Lab:__ Variable = length of the ruler 1a) We will be able to conclude whether or not the length of the ruler hanging off of the table directly relates or indirectly relates to the height of the launched penny. 1b) We will record the height of the penny vs. the amount of the ruler hanging off of the table (in centimeters). 1c) A ruler, a penny and a meter stick 1d) We will record it in a data table comparing the two variables to each other. 3. __Conclusion:__ The height of the penny is directly proportioned to the length of the ruler off of the table. As the length off of the table increases, so does the height of the penny.
 * Investigate:**
 * **Trial** || **Height of Penny (cm)** || **Length of Ruler (cm**) ||
 * 1 || 60 || .5 ||
 * 2 || 110 || 1 ||
 * 3 || 130 || 1.5 ||
 * 4 || 165 || 2 ||
 * 5 || 180 || 2.5 ||

__Kinetic Energy:__ energy associated with motion > KE = 1/2mv 2 __Gravitational Potential Energy:__ the energy an object possesses because of its vertical position from the earth > GPE = mgh __Potential Energy:__ energy associated with position __Law of Conservation of Energy:__ energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant __Elastic Potential Energy:__ the energy of a spring due to its compression or stretch >EPE = 1/2kx 2 __Work:__ the product of the displacement and the force in the direction of the displacement > W = F x d when it is moving || KE = 1/2mv^2 || it is above the lowest point || GPE = mgh || when stretched or compressed || EPE = 1/2kx^2 k = spring force constant x = distance || distance parallel to the direction of motion || W = Fd ||
 * Physics Talk Summary:**
 * **Type of Energy** || **Description** || **Equation** ||
 * Kinetic Energy || energy possessed by an object
 * Gravitational Potential Energy || energy possessed by an object when
 * Elastic Potential Energy || energy possessed by a spring
 * Work || caused by a force acting over some

1. Force is required for the energy of an object to change 2. The penny gets its energy from the force put on the ruler and then the ruler pushing against the penny. 3. The force his arms use to pull (tension) the poll backwards then reflects forward with the pole vaulter and fly over the bar. 4. Joules
 * Checking Up Questions:**


 * Physics To Go:**

- In Gravitational Potential Energy, the three variables that affect it are mass, gravity and height. So, if the mass and gravity and both less then the height will decrease, and vice versa. Also, using Kinetic Energy (mass and velocity), the more mass, the less velocity. The larger pole will have more mass, which then results in slower velocity. One needs more velocity to reach a higher hight.
 * What Do You Think Now:**

=Chapter 2 Section 9=

- I think that the "hang time" of some athletes defy the pull of gravity because of the amount of force they put into the jump they are making. Whether or not they technically "defy gravity" depends on the person weight, because that directly affects against the gravity pulling them down.
 * What Do You Think:**

__Pre Lab:__ 2. The skater is in the air for 20 frames 3. Amount of time in the air: 2/3 seconds 4. The skater did not actually hang in the air, it is an allusion. 5. Basketball player = 30 frames, 1 second.
 * Investigate:**

__Lab:__ 1a. The work and GPE energy exerted when I jump 1b. We will record starting hip point, bent hip point, distance between ground and shoes when at the highest point in the air. 1c. A meterstick 1d. We will put the data in the equation: Fd = mgh

Calculations: Fd = mgh F(1.99) = (464)(.319) F = 743.8
 * || **Initial Hip Height** || **Bent Hip Height** || **Distance between floor and feet** ||
 * **1** || .934 m || .735 m || .12 m ||
 * **2** || .934 m || .70 m || .19 m ||
 * **3** || .934 m || .60 m || .20 m ||

Fd = mgh F(.234) = (464)(.424) F = 840.8

Fd = mgh F(.334) = 464(.534) F = 741.8

AVG: 775.5 Caluclated: 950.23 % error = 18.4%

Graph:


 * Physics Talk Summary:**

1. The energy comes from the force against your feet from the floor. EPE - the spring of your legs pushing against the floor 2. The energy during your lunch you have GPE in the air and at the peek of the jump you have GPE again. 3. Work
 * Checking Up Questions:**


 * Physics To Go:**


 * Physics Plus:**

- A world-class figure skater does not defy gravity to remain in the air long enough to finish a trick. It all relies on the amount of energy in each step of the triple-axel and the are never just hanging in the air not moving at all. There is always an energy pushing or pulling or somehow reacting on the athlete to let them finish a triple-axel.
 * What Do You Think Now:**